"May I have cake, please?"
Translation:Ga i gacen, plîs?
So why doesn't this accept "os gwelwch yn dda" or any of the other forms of please in the answer? I'm not entirely sure how I'm supposed to know which is correct, and the one in my comment is the one I am used to, is it okay to use this generally?
Depending on how the sentence comes up and how you are able to answer, you may be able to use a 'report' button to suggest 'my answer should be accepted'. Duo can then take a look and, if your answer is a correct one, add it to the list of acceptable alternatives. Apparently, that way is an easy one for the course team to use.